Printing plate



Patented Feb. 4, 1941 UNITED STATES PATENT OFFICE Masa, assignors toWilliam Craig Toland,

Brookllne, Masa, as trustee No Drawing. Application July 23, 1940,Serial No. 347,044

26 Claim.

This invention relates to planographic printing plates and is acontinuation in part of earlier applications, Ser. No. 311,294, filedDecember 28, 1939 and Ser. No. 170,762, filed October 25, 1937.

In the preparation of planographic printing plate surfaces, it is nowcustomary, in most cases, to employ metal plates. The surfaces of theseplates are required to be roughened by a graining operation whichrenders the surfaces capable of retaining films of water and becomingthereby grease-repellent. The graining operation increases to anobjectionable extent the cost of preparation of plates by both the timeand labor required and the equipment employed. In addition to its cost,the graining operation is objectionable due to the fact that platesprepared by it must be subjected to etching or gumming operations bothduring the preparation and operation of the plate. Furthermore,satisfactory grained metal lithographic surfaces can be prepared on onlya few relatively expensive metals.

It is a chief object of the present invention to improve planographicprinting plates and to devise novel water-receptive portions of aplanographic plate surface which may take the place of grained platesurfaces and eliminate some etching and gumming treatments now requiredto be carried out in connection with grained metal plates, and which maymake possible the use of various metals and other materials to comprisea base for a printing plate.

The invention also aims to present a combination of materials adapted toprovide a coated body which gives printing effects equivalent to, orbetter than, the efiects obtained with lithographic stone printing.

It is a further object of the invention to provide a colloid plate ofnovel limited water-receptive character, and generally to make availablea simple, cheap and efficient printing plate capable of effectingimproved printing quality.

The nature of the invention and its objects, will be more fullyunderstood from the following description, and the novel features willbe more particularly pointed out in the accompanying claims.

In making planographic printing plates, as indicated above, it iscustomary to provide a metal support and to rely on grained metalsurfaces for retaining water and repelling greasy inks in thenon-printing portions of the plate. The usual practice is to employ themetals aluminum arid zinc to comprise the support and to grain-one sideof the metal so that it may retain water by capillary attraction. Thisis expensive and slow,

and involves tying up of many thousands of metal plates which have to bestored and which require therefore a large amount of space. In addition,graining machinery is costly and represents a very considerableinvestment of money. It may therefore be seen that it is highlydesirable to avoid the grained plate construction in preparing aplanographic printing surface.

In accordance with our invention, we employ a synthetic hydrophilicresin in a film state to take the place of the grained metal surfacesdescribed. We apply a thin layer of a resin, as for example from asuspension of polyvinyl alcohol (3% solution) on a suitable support.This film is allowed to set and is then moistened. Printing portions arethereafter prepared on a film, as for example by the albumin process.

This albumin process consists in applying on the moistened film acoating material which consists of albumin and a material sensitive toactinic light such as ammonium bichromate, or other chromic salt. Thefilm of sensitized albumin is allowed to dry and is then exposed under anegative to actinic light, whereby the exposed portions of the albuminbecome hardened and grease-receptive. The plate is then rolled up with adeveloping ink, held under running water and developed by lightlyrubbing asviith a pledget of cotton to remove the ink and albumin fromthe non-exposed areas. This efiects printing portions of albumin whichare sensitized to grease and non-printing surfaces of hydrophilicmaterial which retain water by absorption and are thereby desensitizedto grease.

It is pointed out that by applying the coating, the entire step ofgraining with all of its attendant difliculties is avoided. In addition,due to the hydrophilic character of the film described, moisture isretained by absorption, and capillary effects such as are required inthe development c of a hygroscopic surface on a grained metal plate,need not be resorted to. With the hydrophilic plate surface, certainetching and gumming' operations required in connection with the use ofgrained metal plates may be eliminated or greatly reduced. Thehydrophilic film functions somewhat in accordance with the principle ofa colloid printing plate by absorbing water in the manner other thanalbumin, as bichromated gum and the like.

Various materials may be utilized to comprise a suitable support, as forinstance metals of many types, plastic compositions, paper and the like.It will be observed that this is a' definite advantage since with aplate of grained surface only metal may be utilized and only a fewmetals such as zinc and aluminum are satisfactory.

Various other solution strengths of polyvinyl alcohol may be employed,as 5% and 10% solutions and others. In addition to the polyvinyl alcoholresin cited as a suitable coating material for effecting non-printingportions of a plate, certain other resins may be employed as vinylresins, such as vinyl acetates, halides, esters, copolymers of esters,ethers, ketones, alcoholates, and the like. Also we may employ somesynthetic resins of a normally hydrophilic character and particularlysynthetic hydrophilic colloids which may be put into solution orsuspension and thus may be readily coated on a support to comprise afilm, which will absorb water in a suitable manner for forming thenon-printing portions of a planographic printing plate. Such films maycomprise certain synthesized materials obtained from hydrocarbons,phenols, aldehydes, ketones,

amines, natural resin acids, polyhydric alcohols" and polybasic acids,vinyl compounds, rubber, sulphur and fatty oils. Only those materialsobtained from the above noted reactants which, without dissolving, arehydrophilic in a proper degree for meeting lithographic printinglimitations, or which may be made so by treatment with reagents, aresuitable for purpose of coating in accordance with this invention andare intended to be included.

A few such resins from which plates less desirable than vinyl plates maybe made comprise (a) a product obtained from heating to 100 C. 150 partsof diethylene glycol and 70 parts of boric acid together with 80 partsof borax with agitation (aqueous solution); (1)) a product obtained fromtreating polyvinyl alcohol with an aldehyde and a substance capable ofcondensing with the aldehyde, as a phenol; (c) a product obtained bytreating a vinyl ester-aldehyde with another aldehyde; (d) a productobtained by heating methylolurea with a compound containing at least twofree hydroxyl groups (aqueous solution); (e) and a condensation productresulting from treating aryl sulphonamido carboxylic acid amide withformaldehyde (aqueous solutions).

A further aspect of our invention deals with a plate having modifiedhydrophilic non-printing portions comprising a hydrophilic materialcombined with a chromic salt such as ammonium bichromate, particularreference being had to polyvinyl alcohol and other vinyl compounds.

The non-printing, portions of this modified plate material shoulc'lnotbeconfused with printing portions of plates obtained from hardeningalbumin or other coatings withfiammonium bichromate where the ammoniumbichromate has been employed as: asensiti'zing agent for exposure toactinic light to render the various colloids hard and grease-receptive.

According to our improved'method of treating a hydrophilic coating witha chromic salt, -we provide for directly mixing a solution of a salt,such as ammonium bichromate, with a'solution of polyvinyl alcohol andallowing a film of the product to dry without necessarily employing anyaction of light or other agents whatever,

although the action of light or other agents in some instances may notbe objectionable. Our method is based upon the discovery that the use ofa chromic salt, and in particular ammonium bichromate, with a vinylcompound such as polyvinyl alcohol in substantially any proportion,while toughening a film of the vinyl compound, fails to result in thedevelopment of a product which is completely water-repellent and henceadapted to receiving grease. This is the opposite case of that whichresults from combining bichromate with most colloids such as albumin,glue, and the like. These colloids are quickly hardened by bichromate toan extremely waterresistant mass which is easily rendered grease-Qreceptive so that it would cause objectionable smurring in' a plate.Heretofore, it has been considered impossible to allow ammoniumbichromate to remain in a hydrophilic colloid film if water receptivitywas'desired, for the reason that when combined with colloid materials,the bichromate would continue to harden at a slow rate until sooner orlater grease-receptive surfaces were formed. This aspect of'ourinvention is based essentially on the discovery that the bichromate canbe used to limit water-receptivity of a hydrophilic colloid without itsnecessarily developing grease-receptivity, especially when the treatedcolloid is moistened before possible contact with greasy orgrease-forming materials.

The desirable hardening effect noted may result from the reaction whichtakes place upon the mere admixture oi. the bichromate and the colloid.It maybe expedited, however, by subdecting the mixture to light, heat,and/or pressure. Although light is effective as an agent for expeditingthe reaction, we prefer not to use it in reacting the chromic salt witha vinyl compound such as the alcohol, for the reason that it renders thefilm dark yellow in color. Maintenance of the translucent character ofthe film,

in a plate or in the print on a plate, is advisable,

as it facilitates correction of errors, as well as preparation andhandling of the plate.

A desirable treatment of a hydrophilic synthetic material to decreasewater-receptivity may also be effected with a copper salt such as cupricchloride. We may desire to use certain other reagents to accentuate theaction of the salt used, as for example ferric chloride or ferric.sulphate mixed with a bichromate solution. It may further be desired toemploy these and other agents, as heat and pressure and others, fortreating other hydrophilic materials of the class referred to above. Inemploying the polyvinyl alcohol and the ammonium bichromate, variousproportions may be employed of which one specific example consists inthe following amounts:

- Oz. 5% polyvinyl alcohol suspension 7 Ammonium bichromate 1 tions.Either with orwithout the ferric chloride, suitable water-receptivefilms may be quickly obtained from this mixture. Thicker and more slowlydrying films may be formed from mixtures of larger proportions of theresin.

The grained metal surfaces of zinc and aluminum plates, for which thecoatings of the invention are a substitute, were designed to take theplace of lithographic stone. Certain other substitutes have also beenattempted from time to time by combining clay, or other fillermaterials, with a binder such as a colloid, or a cementitious material,or other type of bonding agent. Such mixtures are intended to form asuspension which may be coated upon a suitable base. In a coated state,the clay particles are designed to form a stone-like body having a waterabsorptive character generally resembling that of lithographic stone.Attempts to coat such suspensions have been unsuccessful. One reasonconsists in the fact that the suspensions cannot be prepared of auniform consistency suitable for forming smooth coatings. These mixturestend to coagulate and form a lumpy mass which prevents uniformapplication. Also, the dried coatings do not retain water in asatisfactory manner after being subjected, for a short time, to use on apress,

and to the action of grassy inks. This is particularly due to thebonding agents, heretofore employed, becoming sensitized to grease inthe non-printing portions of a plate surface which causes smurring orother undesirable ink transfer.

Another feature of the invention consists in the use of a hydrophilicmaterial, of which the polyvinyl alcohol is particularly exemplary, withclays or other fillers to provide a suspension having a consistency Welladapted to being uniformly spread over a base, and to forming asatisfactory printing surface which gives printing quality resemblingthat obtained from printing with lithographic stone. The colloidalcharacter of polyvinyl alcohol, in particular, enables this substance tobecome intimately incorporated with the tiny filler particles whichprovides a suspension of highly uniform consistency, well adapted toforming a smooth coating and to being spread out in a very thin state.

In a dried coating of a mixture as described, the hydrophilic materialfunctions as a bonding agent interposed in and around the fillerparticles, and also continues to accept water in the usual manner. Thiseffects a permanent water reservoir between the filler particles whichis not affected by any exposure to grease and which makes possible longlife operation of the plate. At the same time, the filler particles lenda certain amount of hardness to the hydrophilic materials, may beutilized to reduce and also to maintain substantially constant theamount of water retained in any given surface area, and may provide amild grain in the surface greatly resembling the grain of lithographicstone.

By the addition of a filler, the hydrophilic materials may be renderedmore adhesive and, in some instances, such suspensions will stick firmlyto materials on which the hydrophilic material alone cannot be bonded.One example of such a substance is rubber. The hardening effect of afiller such as clay may in some cases eliminate the use of the varioushardening agents already discussed, and is further useful infacilitating penetration and retention of materials making up theprinting image portions of the plate, and in inking such portions. Withsome proportions of filler and hydrophilic material, swelling in thenon-printing portions of a plate prepared from the mixture issubstantially reduced or eliminated.

Preferred filler materials which may be placed in suspension withhydrophilic materials are calcium carbonate, kaolin and china clay.Others may be desired to be employed, as for example feldspar,fluorspar, barium sulphate, calcium chloride, and the like. A preferredhydrophilic material is polyvinyl alcohol. Hydrophilic substances suchas vinyl compounds and others above referred to may also be employed.Various proportions of the hydrophilic material and filler may be used.One example thereof consists in the following mixture:

5% polyvinyl alcohol pt 1 China clay oz 2 Other amounts in the sameproportion may be resorted to. If desired, the various hardening agentsrecited above may be desired to be employed with the mixture in somecases. Also, various treatments may be given a coating formed from thesemixtures. For instance, a coating may be subjected to etching treatmentsif desired, or it may be subjected to immersion in various preservingmaterials or other reagents.

It will be seen that the invention provides improved printing plates,greatly superior to plates having grained surfaces for retainingmoisture by capillarity. The hydrophilic coating, either with or withoutfillers, can be more cheaply and quickly prepared, and may effectimproved printing quality. Various materials may be used to support thecoating, and limitation to use of zinc or aluminum is obviated. Thehydrophilic character of the coating is limited by several means to ahighly satisfactory point. If the coating without filler is employed ona grained surface, it should be noted that it conforms to such grain,thereby presenting a secondary grained surface of softened or modifiedcharacter which in some instances may be employed to effect finerhalftone quality of printing. This is particularly the case where apaper support is used which presents a very fine grain for the coatingto conform to. Various other graining effects such as roughening topromote water-receptivity by capillarity, may be resorted to, with thecoatings. The addition of fillers in the manner described furtherenhances the desirable water receptive character of the hydrophilicmaterials generally, and provides a type of printing which is anexcellent substitute for lithographic stone printing.

The term hydrophilic as employed in the specification is intended tomean "water-absorptive and not water-soluble. Where the materialreferred to may occur in both water soluble and water-absorptive states,as for example polyvinyl alcohol, which is soluble in hot water butwhich in a film state may be rendered only water absorptive to coldwater, it isintended that the term hydrophilic refer to the material ina water-absorptive state.

While we have disclosed preferred reagents, materials and procedures, itshould be understood that various changes and modifications may beresorted to therein, in keeping with the spirit of the invention asdefined by the appended claims.

Having described our invention, we claim:

1. As a new article of manufacture, a printing plate presentingwater-receptive areas comprising a polyvinyl alcohol.

2. As a new article of manufacture, a colloidal printing plate havingprinting areas and nonprinting areas occurring therein, saidnon-printing areas comprising polyvinyl alcohol in a water- 5 receptivestate.

3. As a new article of manufacture, a colloidal printing plate havingprinting areas and nonprinting areas occurring thereon, saidnon-printing areas comprising that hydrophilic product obtained fromhardening polyvinyl alcohol with ammonium bichromate in the presence offerric chloride.

4. As a new article of manufacture, a colloidal printing body havingprinting areas and nonprinting areas occurring therein, saidnon-printing areas comprising hydrophilic polyvinyl alcohol and theexposed surfaces of said areas being roughened to further promotewater-receptivity by capillary action.

5. A colloidal printing plate comprising a base and a material coatedover said base, said material presenting printing areas and non-printingareas and said non-printing areas comprising water-receptive polyvinylalcohol.

6. A colloidal printing plate comprising a base and a coating ofpolyvinyl alcohol on said base, said polyvinyl alcohol coatingpresenting selective non-printing areas having a substantially fixeddegree of water receptivity.

and a film of polyvinyl alcohol coated on said base, said polyvinylalcohol coating presenting hydrophilic non-printing" areas, thepolyvinyl alcohol comprising the non-printing areas being in a state ofpolymerization of such degree as to provide a water receptivitysubstantially equivalent in uniformity and deflniteness of moistureretention to the water receptivity of a grained metal lithographicprinting plate.

8. As a new article of manufacture, a colloidal printing plate havingprinting areas and nonprintlng areas occurring thereon, saidnon-printing areas comprisinga hydrophilic product resulting fromhardening polyvinyl alcohol with ammonium bichromate in the presence offerric sulphate.

9. As a new article of manufacture, a printing plate presentingwater-receptive areas comprising a vinyl compound.

10. As a new article of manufacture, a printing plate presentingwater-receptive areas comprising co-polymers of vinyl esters.

11. As a new article of manufacture, a printing plate presentingwater-receptive areas comprising polyvinyl alcohol and ammoniumbichromate.

12. As a new article of manufacture, a printing plate presentingwater-receptive areas comprising polyvinyl alcohol, ammonium bichromateand ferric chloride.

13. As a new article of manufacture, a printing 7. A colloidal printingplate comprising a base plate presenting water-receptive areas includinga polymerized vinyl compound and a chromic salt.

14. As a new article of manufacture a printing plate presentingwater-receptive areas comprising a vinyl compound, a chromic salt and asalt selected from the group consisting of ferric chloride, ferricsulphate and the like.

15. As a new article of manufacture, a printing plate presentingwater-receptive areas comprising vinyl acetate.

16. As a new article of manufacture, a printing plate presentingwater-receptive areas comprising a vinyl ester.

17. As a new article of manufacture, a printing plate presentingwater-receptive areas comprising a vinyl ether.

18. As a new article of manufacture, a printing plate presentingwater-receptive areas comprising a vinyl compound and cupric chloride.

19. As an article of manufacture, a printing plate presentingwater-receptive areas which comprise a mixture of a vinyl compound and afinely divided clay-like material.

20. As an article of manufacture, a printing plate presentingwater-receptive areas comprising a mixture of a hydrophilic vinylcompound and a filler.

21. As an article of manufacture, a printing plate presentingwater-receptive areas comprising a mixture of polyvinyl alcohol and aflller.

22. As an article of manufacture, a printing plate presentingwater-receptive areas comprising a mixture of a hydrophilic vinyl resin,a finely divided, clay-like filler, and a hardening agent.

23. Asan article of manufacture, a printing plate presenting a surfacecoating consisting of a mixture of a hydrophilic vinyl resin and afiller, a grease-receptive printing image impregnated in the fillerand.resin mixture to form printing and non-printing portions of apianographic printing surface.

24. As an article of manufacture, a printing plate presentingwater-receptive areas comprising a vinyl resin. an ingredient forhardening the vinyl compound and an ingredient for imparting porositythereto.

25. As an article of manufacture, a printing plate comprising a base, acoating on said base consisting of a mixture of a water-receptive vinylcompound and an ingredient for reducing swelling of the vinyl compound,printing portions supported on the said coating and bonded to the saidingredient and vinyl compound.

26. As an article of manufacture a printing plate presentingwater-receptive areas comprising a hydrophilic film of a vinyl compoundand an ingredient for modifying the water-receptivity of the vinylcompound.

WILLIAM CRAIG TOLAND. ELLIS BASSIST.

